Powder inhalers are being increasingly used nowadays as dosing and inhaling apparatus in the treatment of asthma by inhalation. This is because of objections, on ecological grounds, to conventional 2.times. metered dose aerosols because they have used halogenated hydrocarbons as the propellant gas.
A further disadvantage of 2.times. metered dose aerosols is that the patient must be able to coordinate the release of spray and inhalation. This is not always possible during an acute asthma attack in which the patient is under great stress. Powder inhalers eliminate the need to coordinate inhalation and spraying, since the air inhaled by the patient activates the dosage release.
In conventional powder inhalers (for example as disclosed in Published European Patent Application EP-A 406 893) each dose of the active substance is contained in a single hard gelatin capsule. The capsule is inserted in an apparatus where it is punctured by several pins. The contents of the capsule are released and carried along by the flow of air inhaled by the patient. They are then transported to the lungs of the patient.
This type of powder inhaler has the disadvantage that a diluent, such as lactose, has to be added to the active ingredient to fill the capsule and to ensure dosage accuracy. In some patients inhalation of the finely distributed lactose powder can lead to airway irritation.
Moreover there is no guarantee that the punctured capsule is completely emptied and that its content is available to the patient. What is more, there is a danger of fragments of capsule being inhaled as well.
German Patent DE-P 27 04 574 discloses an inhaler for a pharmaceutical enclosed in a capsule where the capsules are stored in a rotatable magazine that is moved forwards by rotating the outer casing of the inhaler.
Apparatus that dispenses with capsules may avoid the above disadvantages. Thus, for example, the Turbuhaler.RTM. manufactured by Astra works without lactose as an auxiliary substance and the pharmaceutically active substance is inhaled directly. Each apparatus permits withdrawal of two hundred doses. The pharmaceutical is stored in a storage container in the form of spherical aggregates of a micronized powder. During inhaling, these aggregates disintegrate into the micronized powder which is respirable.
Administration of the powder is aided by a rotatable dosage disk. The spherical agglomerate of the pharmaceutical is pressed from above into a group of four measuring openings which determine the amount of the granulate to be released. The granulate is measured volumetrically.
The dosage disk is rotated further and, with the four dosage holes filled, reaches a part of the inspired air flow and the active substance is torn out of the dosage holes. The spherical aggregates are divided up in the spiral-shaped flow of the mouthpiece and inspired as micronized powder.
A disadvantage of the Turbuhaler.RTM. is that the dosage holes can become blocked and the dosage accuracy can decrease progressively as the apparatus is used. Furthermore a not inconsiderable amount of the pharmaceutical accumulates in the mouthpiece with the number of dosages released. This constitutes a risk for the patient, since there is a danger that too much of the pharmaceutical will be inspired at once.
Published European Patent Application EP-A 407 028 describes a powder inhaler that scrapes a measured amount from a compact supply of pharmaceutical using a scraper and allows this amount to be transferred into a cyclone chamber by the airstream of the patient. The mixture layered in the cyclone is inspired by the patient.
Published European Patent Application EP-A 387 222 describes an electronically controlled device for the release of a pharmaceutical which responds to the noise created by the flow of the inspired air and releases a dose from the supply of medication.
Published European Patent Application EP-A 237 507 describes a powder inhaler with impact surfaces that divide up the supply of medicament released from the dosage container.
Published European Patent Application EP 69 715 describes a powder inhaler activated by the stream of air inspired by the patient. It is possible for the inspired air stream from a dosage device, which can be rotated into the inspired air stream, to draw a volumetrically measured amount of pharmaceutical with it.